This is a continuation of a long term project to understand the cellular basis of primate vision, and especially color vision, by studying the electrical responses of single cells in the retina and at higher levels of the visual system in monkeys. The current research attempts to understand what information is transmitted to visual cortex by each of a relatively small number of parallel retinal and subsequently retinogeniculate channels which subserve each unit area of visual space. The experiments will use visual stimuli in which spectral (wavelength) and effective energy (brightness) contrast can be independently controlled and in which the spatio-temporal properties of these stimuli can be varied in a sophisticated manner. The experiments will determine what class of stimuli are most effective for each of at least three separate classes of retinal ganglion cells: one class subserving the short wave sensitive cone mechanism and at least two quite different classes of cells subserving the other two cone mechanisms in primate retina, a so called phasic (Y-like) system which shows no over opponent interactions between these two cone mechanisms and a second so called tonic (X-like) system which often shows such opponent interactions. The experiments can ultimately lead to visual stimuli that activate each of these retinal channels exclusively of the other two. This can produce new approaches to decipher the ultimate targets and function of these subsystems in higher visual centers and to a better understanding of the mechanisms of color vision. The research will attempt to show unequivocally that the Hering-like opponent color model of color vision does not exist at the retino-geniculate pathway. Intracellular experiments will also be performed on retinal cells in order to understand the presynaptic circuitry that produces this parallel system of functionally different ganglion cells. The information from both sets of experiments can lead to new ways of identifying and examining the function of these parallel visual pathways in human subjects and patients by psychophysical and electrophysiological techniques.